1. Field of the Invention
The present invention relates to a method and an apparatus of producing a thin film of metal oxide or the like on a surface of a substrate.
2. Description of the Related Art
Thin films of metal oxides are generally used as oxide dielectric and insulating films of SiO2 and Ta2O5, high dielectric and ferroelectric films having a Perovskite structure represented by ABO3, in particular, of BaTiO3, Ba(Ti,Hf,Zr)O3, SrTiO3, (Ba,Sr)TiO3, (Ba,Sr,Ca)TiO3, PbTiO3, PbZrO3, Pb(Nb,Ti)O3, Pb(Zr,Ti)O3, PLZT, YMnO3, and (La,Sr)MnO3, ferroelectric films having other structures, of SrBi2Ta2O, SrBi2(Ta,Nb)2O9, Sr2(Ta,Nb)O7, (Sr,Ba)Nb2O6, SrTa2O6, Bi4Ti3O12, and Bi2SiO5, electrode films of RuO2, RuO4, SrRuO3, and IrO2, and buffer films of Y2O3, CeO2, ZrO2, and (Ce,Zr)O2 for memory materials of MFIS-FET, MFMIS-FET structures and films exemplified by ferroelectric films.
Thin films of metal sulfides are used as thin films for use in light-emitting elements. For example, thin films of metal sulfides are used as inorganic EL films including thin films for blue light-emitting elements, of CaGa2S4+Ce, ZnS+Tm, SrS+Ce+blue filter, and SrS+Cu, thin films for green light-emitting elements, of ZnS+Tb, CaS+Ce, ZnS+Mn+green filter, and SrGa2S4+Eu, thin films for red light-emitting elements, of SrS+Sm, CaS+Eu, and ZnS+Mn+red filter, and protective films for light-emitting films, of ZnS.
Thin films of metal nitrides are generally used as nitride dielectric and insulating films of SiN and SiON, electrode films of TaN and TiN, and barrier films of TaN, TaSiN, TiN, TiSiN, WN, WSiN, and (Ti,Al)N.
Heretofore, thin films of metals such as metal oxides have generally been manufactured by an evaporation process and a CVD process. According to the evaporation process, a desired material is evaporated to deposit a film on a substrate in a vacuum whose pressure is 10xe2x88x922 Pa or lower. According to the CVD process, a thin film of a material produced by thermal decomposition or chemical reaction is precipitated on a substrate.
However, the production of thin films of metals according to the evaporation process or the CVD process requires an expensive, large-scale evacuating apparatus, which needs a large expenditure of initial expenses. In addition, the evaporation process or the CVD process requires a relatively long period of time to grow the desired film, and causes the substrate to be held at a high temperature during the film growth. While it has been attempted to produce thin films of metals according to a sol-gel process, it has proven difficult to achieve a sufficient bonding strength between the substrate and the thin film.
It is therefore an object of the present invention to provide a method and an apparatus of inexpensively and quickly producing a thin film of metal that is bonded to a substrate with a sufficient bonding strength, without the use of an expensive, large-scale evacuating apparatus.
According to a first aspect of the present invention, there is provided a method of producing a thin film of metal or metal compound, comprising: preparing an ultrafine particle dispersion liquid containing ultrafine particles at least partly made of metal, said ultrafine particles being dispersed into a given organic solvent; applying said ultrafine particle dispersion liquid to a surface of a substrate; drying said ultrafine particle dispersion liquid to leave metal or metal compound particles on said substrate; and heating said metal or metal compound particles to join said metal or metal compound particles together.
According to a second aspect of the present invention, there is provided a method of producing a thin film of metal or metal compound, comprising: preparing an ultrafine particle dispersion liquid containing ultrafine particles at least partly made of metal, said ultrafine particles being dispersed into a given organic solvent; applying said ultrafine particle dispersion liquid to a surface of a substrate; heating said ultrafine particle dispersion liquid to leave metal or metal compound particles on said substrate and join said metal or metal compound particles together; and annealing said joined metal or metal compound particles.
According to a third aspect of the present invention, there is provided a method of producing a thin film of metal or metal compound, comprising: preparing an ultrafine particle dispersion liquid containing ultrafine particles at least partly made of metal, said ultrafine particles being dispersed into a given organic solvent; applying said ultrafine particle dispersion liquid to a surface of a substrate; drying said ultrafine particle dispersion liquid to leave metal or metal compound particles on said substrate; heating said metal or metal compound particles to join said metal or metal compound particles together; and annealing said joined metal or metal compound particles.
According to a forth aspect of the present invention, there is provided an apparatus of producing a thin film of metal or metal compound, comprising: a dispersion liquid supply device for applying ultrafine particle dispersion liquid containing ultrafine particles at least partly made of metal, said ultrafine particles being dispersed into a given organic solvent to a surface of a substrate; a drying mechanism for drying said ultrafine particle dispersion liquid to leave metal or metal compound particles on said substrate; and a heating device for heating said metal or metal compound to join said metal or metal compound particles together.
With the above methods and an apparatus, ultrafine particles uniformly dispersed in a organic solvent and at least partly made of metal are uniformly coated on a surface of a substrate, and all organic materials are heated and decomposed to join metal or metal compound particles, producing a thin film of metal bonded to the substrate with a sufficiently large bonding strength. The thin film may then be annealed into a crystalline state.
The metal or metal compound particles may be heated or annealed in an oxidizing gas atmosphere to produce a thin film of metal oxide. The thin film of metal oxide may be made of SiO2, Ta2O5, BaTiO3, Ba(Ti,Hf,Zr)O3, SrTiO3, (Ba,Sr)TiO3, (Ba,Sr,Ca)TiO3, PbTiO3, PbZrO3, Pb(Nb,Ti)O3, Pb(Zr,Ti)O3, PLZT, YMnO3, (La,Sr)MnO3, SrBi2Ta2O9, SrBi2(Ta,Nb)2O9, Sr2(Ta,Nb)O7, (Sr,Ba)Nb2O6, SrTa2O6, Bi4Ti3O12, Bi2SiO5, RuO2, RuO4, SrRuO3, IrO2, MFIS-FET,Y2O3, CeO2, ZrO2, or (Ce,Zr)O2.
The metal or metal compound particles may be heated or annealed in a hydrogen sulfide atmosphere to produce a thin film of metal sulfide. The thin film of metal sulfide may be made of CaGa2S4+Ce, ZnS+Tm, SrS+Ce, SrS+Cu, ZnS+Tb, CaS+Ce, ZnS+Mn, SrGa2S4+Eu, SrS+Sm, CaS+Eu, ZnS+Mn, and ZnS.
The metal or metal compound particles may be heated or annealed in a nitriding gas atmosphere to produce a thin film of metal nitride. The thin film of metal nitride may be made of SiN, SiON, TaN, TaSiN, TiN, TiSiN, AlN, WN, and ZrN.
The metal may comprise at least one metal selected from the group consisting of Si, Ta, Ca, Sr, Ba, Ti, Bi, Pb, Nb, Y, Mn, Al, Hf, Zr, Ce, Ir, Ru, Zn, Mg, La, Ga, Tm, Cu, Tb, Eu, Sm, and W.
In a preferred aspect of the invention, an apparatus further comprising a supplementary drying device for drying the ultrafine particle dispersion liquid which has not evaporated by said drying mechanism. Therefore, an organic solvent is completely dried by the supplementary drying device to prevent the formation of voids.
The above and other objects, features, and advantages of the present invention will become apparent from the following description of preferred embodiments of the present invention which are given by way of example.